EP0368751B1 - Finished diffractive contact lens - Google Patents

Description

The present invention relates to the field of contact lenses intended to be placed on the cornea of the eye.

Specialists have for several years considered developing diffractive lenses (see for example EP-A-0 064 812, US-A-4 637 697 or also the patent application FR-88 06699 filed on May 19, 1988).

The engraved diffractive contact lenses, as illustrated in the appended FIG. 1 are generally formed from a component 10 with two diopters 14, 16, one of which has a zoned Fresnel network, that is to say a series of structures 17₁, 17₂, 17₃ ... in relief, annular, concentric around the axis 12 of the lens.

The structures 17 generally all have the same profile. They also have the same surface area. The external radii of the different structures therefore evolve according to a geometric progression of the type: √K r, where r denotes the external radius of the central structure and K denotes successive integers.

The focal lengths fn of the diffractive component thus formed are equal to: fn = r² / 2n λ where
r = the external radius of the central structure,
n = the diffraction order,
λ = the wavelength considered.

The diffraction order n = +1 can be obtained with relief structures of the sampled kinoform type, that is to say structures each having a profile composed of M levels, with M greater than 2, phase-shifted by 2 π / M.

The diffraction orders n = +1 and n = -1 can be obtained simultaneously with relief structures of the niche function type generating a phase shift of π.

The performance of an etched diffractive contact lens, in terms of diffraction efficiency, depends first of all on the product: etching depth x difference of the indices on either side of the etched diopter. This product is generally called "optical etching depth".

The optical etching depth is generally between once and 1.5 times the average wavelength of use (of the order of 0.5 μm).

To reduce the precision constraints on the production of the component (i.e. increase as much as possible the engraving depth) it quickly became necessary for specialists to place the engraved diopter on the cornea side of the eye (the difference between indices n₁ - n₃ being less than n₁ - n₂ by calling n₁ the index of the material forming the component, n₂ the index of air and n₃ the index of tears).

We will usefully refer to the aforementioned prior documents to fully understand the structure and function of the etched diffractive contact lenses.

It is found in practice that these lenses have not been subjected to large-scale industrial exploitation.

This seems to be due to the fact that despite their attractive theoretical properties, etched diffractive contact lenses have crippling drawbacks.

On the one hand, the etched diopter 16 which has sharp edges which almost necessarily have to be placed on the cornea side of the eye, as indicated above, the wearing of engraved diffractive contact lenses quickly leads to irritation.

On the other hand, the functioning of the etched diffractive contact lenses varies widely depending on the hydration conditions of the etched diopter.

In addition, the presence of engravings on the internal face of the lenses is likely to rapidly cause a deposit of proteins and fats contained in the lacrimal fluid, that is to say to cause a fouling of the internal face of the lenses resulting in a reduction of the diffraction efficiencies.

Document US-A-4210391 describes an engraved diffractive contact lens comprising an optical component delimited by two dioptres: one smooth concave placed on the side of the cornea of the eye, the other convex engraved, and a layer of an optically transparent material which has a smooth outer surface and is placed on the engraved diopter to immerse the engraving.

Document US-A-4055378 describes a non-diffractive contact lens provided with streaks of very shallow depths on its main convex and concave faces, with the aim of obtaining different contact angles for each of these two main faces, and by therefore different hydrophilic characteristics, superior on the main convex face.

The object of the present invention is to improve known diffractive contact lenses, in particular by lowering the required etching precision.

To this end, the present invention provides an etched diffractive contact lens comprising an optical component delimited by two dioptres: one smooth, the other etched, and a layer of an optically transparent material and having a smooth outer surface, placed on the engraved diopter so as to immerse the engraving, characterized in that the smooth diopter is convex, while the engraved diopter is concave and placed on the side of the cornea of the eye, and that the refractive index of the material forming the layer which immerses the engraved diopter is greater than the index of the lacrimal fluid.

• la figure 1 représente une vue schématique en coupe axiale d'une lentille de contact diffractive gravée classique conforme à l'art antérieur,
• la figure 2 représente une vue schématique en coupe axiale d'une lentille de contact diffractive gravée conforme à la présente invention.

Other characteristics, objects and advantages of the invention will appear on reading the detailed description which follows and with reference to the appended drawings given by way of nonlimiting example and in which:

• FIG. 1 represents a schematic view in axial section of a conventional etched diffractive contact lens according to the prior art,
• 2 shows a schematic view in axial section of an etched diffractive contact lens according to the present invention.

We can see in Figure 2 attached an etched diffractive contact lens, according to the invention, which comprises a conventional component 10 delimited by two diopters 14, 16, including a diopter 16 etched.

The first diopter 14 is formed of a smooth surface, convex towards the outside of the component. The diopter 14 is formed for example of a spherical surface centered on a point placed on the axis 12 of the lens.

The second diopter 16 is supported on a medium surface which is concave towards the outside. The mean surface of the diopter 16 advantageously corresponds to a spherical surface also centered on a point centered on the axis 12 of the lens.

The mean profiles of the diopters 14 and 16 can be adapted to define a basic refractive power to which is added a diffraction power defined by the etched diopter 16.

According to the invention, the lens shown in FIG. 2 further comprises a layer 50 of an optically transparent material placed against the etched diopter 16 to immerse the etching.

The surface 52 of the layer 50 in contact with the etched diopter 16 is therefore complementary to the etching provided in the component 10.

The second surface 51 of the layer 50, directed towards the outside of the lens is smooth and complementary to the external surface of the cornea of the eye.

The layer 50 is made of a material capable of being easily wetted by tears, to avoid any presence of air at the layer 50 / tears interface.

Furthermore, according to an advantageous characteristic, the material making up the layer 50 is hydrophilic. Thanks to this property, the tear fluid is capable of filling any voids left during manufacture between the engraved diopter and the layer 50.

According to another characteristic of the invention, the material making up the layer 50 has a refractive index n₄ greater than the refractive index n₃ of the lacrimal liquid. Thus, the difference in indices obtained n₁ - n₄ being less than the difference in indices n₁ - n₃ which would be obtained in the absence of the layer 50, thanks to the invention, with equal optical depth of etching, the engraving depth.

However, preferably, the index of the material making up the layer 50 is close to the refractive index of the lacrimal liquid, although greater than this index. Thus, in the event that the latter fills any voids present in layer 50 or at the diopter interface etched layer 50, layer 50 attached to the engraved diopter 16 behaves as a substantially homogeneous component.

By way of nonlimiting example, the basic component 10 of index n₁ can be formed from polymethyl methacrylate or from a silicone acrylate copolymer. The added layer 50 according to the invention is advantageously formed of gelatin, collagen or for example of copolymers obtained from methyl methacrylate and n-vinyl pyrolidone, such materials being described respectively in patents EP-0 011 523, FR-2,586,703 and FR-2,370,063.

The layer 50 can be deposited on the engraved diopter 16 by conventional overmolding. As a variant, the layer 50 can be deposited on the engraved diopter 16 according to the conventional technique, known to those skilled in the art, consisting in placing the lens substantially horizontally (i.e. vertical axis and engraved diopter directed upwards), placing a drop of the material intended to compose layer 50 on the upper surface of the lens and centrifuging the whole.

The present invention has in particular the following advantages.

The cornea of the eye is protected by the layer 50 from the edges of the engraved diopter. The lens is therefore better tolerated.

The external surface 51 of the layer 50 can be more easily adapted to the surface of the cornea of the eye than the surface of the engraved diopter.

The permanent presence of the layer 50 in contact with the engraved diopter stabilizes the difference in indices at the interface of the diopter with respect to a temporary lack of hydration.

Likewise, when the material of layer 50 is hydrophilic, the tear liquid being capable of "perfusing" through the material, this liquid can fill any shortages of material, in particular at the etched interface 16 / layer 50. Thus layer 50 appears substantially homogeneous on the optical plane when the refractive index of the material is fairly close to the refractive index of the tear fluid.

The difference in indices n₁ - n₄ being less than the difference in indices n₁ - n₂, the required engraving precision is less high than it would be with an engraved diopter in contact with air. In addition, the difference in indices n₁ - n₄ also being less than the difference in indices n₁ - n₃ when the index n₄ of the layer 50 is greater than the index of the lacrimal liquid, an etching precision is also obtained. required lower than that required for conventional lenses whose engraved diopter is in contact with the cornea of the eye.

For example, when the material forming the base component 10 is polymethyl methacrylate, the index n₁ = 1.49.

The required etching depth is of the order of: 0.5 / (1.49 - 1), ie approximately 1 μm when the etched diopter is in contact with air.

It will be recalled that the etching depth is equal to the ratio between the optical etching depth (between once and 1.5 times the average wavelength) and the difference in the indices on either side of the etched diopter.

The required etching depth is of the order of: 0.5 / (1.49 - 1.34) = 3.33 µm when the engraved diopter is immersed in the tear fluid.

Finally, the required etching depth is of the order of: 0.5 / (1.49 - 1.378) = 4.46 μm when the etched diopter is covered with a layer of hydrated gelatin in accordance with the present invention.

The advantage of precision obtained thanks to the present invention is therefore a factor of 4.5 compared to the non-submerged case whereas it is only 3.3 for a lens immersed in the tear fluid.

It will also be noted that the external face 14 of the lens according to the invention shown in FIG. 2 remains available to be formed with any curvature, or even with several different curvatures depending on the correction sought.

Of course, the present invention is not limited to the particular embodiment which has just been described.

Claims (7)

1. A diffractive contact lens in relief comprising an optical component (10) delimited by two optical surfaces (14, 16) : one (14) which is smooth and the other (16) in relief, and a layer (50) of optically transparent material having a smooth outside surface (51) and placed over the optical surface (16) in relief so as to immerse the relief, characterized by the fact that the smooth optical surface (14) is convexe, while the relief optical surface (16) is concave and provided on the side of the cornea of the eye, and that the refractive index n₄ of the material forming the layer (50) which immerses the relief optical surface (16) is greater than the index n₃ of tear liquid.
2. A diffractive contact lens in relief according to claim 1, characterized by the fact that the material forming the smoothing layer (50) is easily wettable by tear liquid.
3. A diffractive contact lens in relief according to claim 1 or 2, characterized by the fact that the material forming the smoothing layer (50) is hydrophilic.
4. A diffractive contact lens in relief according to any one of claims 1 to 3, characterized by the fact that the refractive index n₄ of the material forming the smoothing layer (50) is close to the refractive index n₃ of tear liquid.
5. A diffractive contact lens in relief according to any one of claims 1 to 4, characterized by the fact that the smoothing layer (50) is based on gelatin or colagen.
6. A diffractive contact lens in relief according to any one of claims 1 to 4, characterized by the fact that the smoothing layer (50) is based on copolymers obtained from methyl methacrylate and n-vinylpyrolidone.
7. A diffractive contact lens in relief according to any one of claims 1 to 6, characterized by the fact that the refractive index of the material constituting the smoothing layer (50) is about 1.378.

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